Study On Spatial-temporal Distribution Characteristics And Prediction Of Drought In Gansu Province Based On Climate Zoning

Drought is one of the major natural disasters facing mankind in the world today.Its occurrence will cause serious and diversified impacts on agriculture,economy and society in different regions and different periods.Gansu Province is located in an ecologically fragile area,with complex climate conditions,high probability and wide range of drought.In order to better study the temporal and spatial variation characteristics of drought in Gansu Province,it is divided into four climate zones according to the climate type and geographical characteristics:the continental climate area of Hexi(Region I),the monsoon climate area in the northern of Longzhong(Region II),the monsoon climate area of Longnan and the south of Longzhong(Region III)and the alpine climate area of Gannan(Region IV).Using meteorological data from26 national meteorological stations in Gansu Province,the standardized precipitation evapotranspiration index at monthly,seasonal,and annual scales(SPEI-1,SPEI-3,SPEI-12)for the past 60 years(1960—2019)was calculated.The spatiotemporal evolution characteristics of drought in Gansu Province in recent 60 years were discussed by means of climate tendency rate,Mann-Kendall mutation test and spatial interpolation;Combined with the mean deviation(MBE),mean relative error(MRE),root mean square error(RMSE)and determination coefficient(R~2),this paper discusses the simulation ability of the multimode aggregate average in the sixth phase of the International Coupled Model Comparison Program(CMIP6)to the temperature,precipitation and SPEI in Gansu Province.Finally,Mann-Kendall mutation test,spatial interpolation and other methods are used to estimate the temperature,precipitation and drought evolution of Gansu Province in the next 2020-2099 years under the four scenarios of SSP126,SSP245,SSP370 and SSP585 in the CMIP6 climate model,The following main conclusions are obtained:(1)The SPEI values of different time scales showed a decreasing trend from the perspective of time process,and the fluctuation range of SPEI values is smaller as the time scale increases.For seasonal factor,in spring,summer and autumn,the SPEI values show a downward trend in fluctuations in all climate regions of Gansu Province.And the downward trend is obvious,indicating a significant drying trend.In winter,the SPEI values show a rising trend in fluctuations in various climate regions,indicating a trend of wetting.Spatially,it showed a humid trend in Region I of Gansu Province,but it was dire in Region II,III and IV of Gansu Province.And in spring,the drought in various climate regions of Gansu Province has an obvious trend of aggravation,followed by summer and autumn,while in winter,the drought has basically slowed down.The frequency distribution of drought occurrence at different levels in different climatic zones in Gansu Province varies greatly and is uneven.The drought frequency of extreme drought is the highest,while the drought frequency of light drought is the lowest,with moderate and severe drought in the middle.(2)From 1960 to 2014,the annual average temperature under the historical measured condition and the simulated condition showed an increasing trend with the passage of time,and the annual average precipitation showed a decreasing trend.The spatial distribution of the variation coefficient CV of temperature and precipitation was basically the same,the average relative error MRE was relatively small,the spatial distribution of SPEI value was highly similar,and the mutation year from drought to wet was 1998.Based on the overall simulation results of temperature and precipitation,it is found that it is scientific to predict the future drought situation in Gansu Province using the multimode set average of CMIP6.(3)In the CMIP6 model,under the SSP126,SSP245,SSP370 and SSP585 scenarios,the temperature and precipitation of Gansu Province in the future 2020 to 2099 will show an increasing trend with the passage of time.In terms of spatial distribution,the climate tendency rate of temperature under each scenario is generally higher in Region I,and the climate tendency rate of precipitation is generally higher in Region III and IV,and the climate tendency rate of temperature and precipitation under different scenarios is from small to large is SSP126,SSP245,SSP370,SSP585.(4)Under the SSP126,SSP245,SSP370 and SSP585 scenarios in the CMIP6 model,Gansu Province will show the development trend of drought in spring,summer and autumn in the coming 2020 to 2099.The mutation years from wet to dry will be concentrated in the middle and early stages of prediction,while the mutation years from dry to wet will be in the middle and early stages of prediction in winter.The mutation years from dry to wet under the SSP585scenario will be in the early stages of prediction,and the other scenarios will be in the middle and early stages of prediction.The frequency of different types of drought is different between different scenarios.Light drought and extreme drought have the highest frequency under the SSP370 scenario,moderate drought has the highest frequency under the SSP245 scenario,and severe drought has the highest frequency under the SSP585 scenario.The frequency of different levels of drought in different climatic regions of Gansu Province under different climatic scenarios is from large to small:light drought,moderate drought,severe drought,and extreme drought.